Beginning with x=3-3y and solving for y, the first step would be to move the constant 3 to the opposite side of the equation by subtracting it from both sides, which leaves x-3 = -3y.
Now divide both sides by the coefficient of y, which is -3 to get (x-3)/-3 = y
This could be rewritten as -(1/3)*(x-3) = y or -x/3 + 1 = y